Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$181.48	12.487%	$204.1414	$204.14	$204.15	$204.10
Purchase #2	$41.82	11.869%	$46.7836	$46.78	$46.80	$46.80
Purchase #3	$111.69	11.829%	$124.9018	$124.90	$124.90	$124.90
Purchase #4	$111.88	10.222%	$123.3164	$123.32	$123.30	$123.30
Purchase #5	$47.50	10.728%	$52.5958	$52.60	$52.60	$52.60
Purchase #6	$180.97	6.556%	$192.8344	$192.83	$192.85	$192.80
Purchase #7	$109.68	13.355%	$124.3278	$124.33	$124.35	$124.30
7 purchase totals =	$785.02		$868.9012	$868.90	$868.95	$868.80